The way you’d do that is to treat the HP company like a bank loan - create a dummy bank account for “hire purchase”, mark the 24k purchase as paid in full from that account, the 5k deposit and any subsequent payments to the HP company would simply be transfers between bank accounts. The (negative) balance on the HP account at any point is the amount outstanding on the loan. Interest would be “money out” of the HP bank account tagged to the relevant nominal (or you could split the bank payment as part interest to P&L and part capital repayment to the HP account).